FP_NAN

From Cppreference

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Defined in header <cmath>
​#define FP_NAN /*implementation defined*/​		(C++0x feature)

The FP_NAN macro expands to an integer constant expression. It represents a type of floating point values and indicates that the value is not-a-number (NaN).

See also

fpclassify (C++0x)	categorizes the given floating point value (function)
FP_INFINITE (C++0x)	indicates infinite floating point value (macro constant)
FP_NORMAL (C++0x)	indicates normal number (macro constant)
FP_SUBNORMAL (C++0x)	indicates subnormal number (macro constant)
FP_ZERO (C++0x)	indicates zero (macro constant)